I saw some good deals on Ebay.
I got my Quantum Replica helmet for free with the purchase of my bike but you're best bet is to try Ebay. They sell for cheap and they're new, too.
I think Arai's are so much comfortable then Shoei's. Of course, my knowledge is limited because those are the only two I've tried on. I've also noticed that Shoei's visors are bigger than Arai's which enables you to see a lot more. Just my take on it.